1. Field of the Invention
The present invention relates to swimming pool filtering systems and more particularly to a system having selectable water circulation rates.
2. Description of the Prior Art
Residental swimming pools have become popular and common place in today's society; however, pool owners are experiencing a substantial increase in pool maintenance costs due to the increased cost of both energy and pool chemicals. It has also been discovered that pools tend to be a nuisance especially during evening hours when the filtering system generates a noise level that is quite obnoxious in a quiet residential area. The low level hum of a filtering system enters open bedroom windows and often keeps restless sleepers awake.
Pool owners have taken several approaches in an attempt to overcome these problems. The most common procedure is to turn off the filtering system during certain periods of the day and in particular during the night time hours. While this procedure eliminates the night time noise and reduces the overall energy consumption, it provides only a false economy and cannot be considered a satisfactory solution since it subjects the pool owner to certain risks. Turning off the filtering system could result in a substantial health hazard since it allows the development of dangerous levels of pollutants.
When the circulating pump is turned off for extended periods of time, there is a substantial risk that algae formations may rapidly overrun the pool. The elimination of this algae requires heavy doses of algae killing chemicals, the cost of which greatly exceeds the savings in energy and the pool cannot be used for a period of time. Normally, an oxidizing agent, such as chlorine, kills the algae and maintains it under control in the pool. However, the algae consumes a certain amount of the oxidizing agent and once the oxidizing agent is consumed in a particular portion of the pool, uncontrolled algae growth is initiated which rapidly spreads throughout the pool. Thus, it is essential that the pool water be continuously circulated to replenish the oxidizing agent that is consumed in remote corners of the pool. It is clear that the pool owner, by turning off the circulating pump, assumes the risk of rapid algae growth and the accumulation of other contaminants in the pool which may require the use of chemicals for repurifying the water, the cost of which would greatly exceed any energy savings.
Certain pool owners have attempted to avoid the algae formation problem by cycling the filter system on and off at 30 minute intervals; however, this starting and stopping of the pump motor is extremely detrimental to the motor and will severely reduce the life of the motor.
For the pool owner that uses a diatomaceous earth filter, turning off the circulating pump causes the filter to lose its cake and necessitates the replacement of the diatomaceous earth at a considerable inconvenience.
Heretofore, an efficient energy saving filter system has not been available to the individual pool owner. Swimmming pool filter systems have been designed using circulating pumps that had sufficient capacity to provide the necessary head to prime the system and sufficient flow to vacuum the pool and clean the pool after a storm. Thus, an efficient system was considered to be one that utilized a pump with just enough capacity to meet these demands and extra capacity resulted in an inefficient system.
One unique problem that faced the designer of a swimming pool filter system was the variable resistance presented by the filter. A clean filter would present a known resistance; however, the resistance increased asymptotically as the filter became dirty. Thus, the designer had to contend with a variable system head curve.
Referring to FIG. 6, there is shown a series of system head curves resulting from increased filter resistance. The graph of FIG. 6 shows curves for the system having Total Head (H) plotted against resulting capacity or Flow Rate (Q). The solid line labeled Total Circulation System Head represents the total system curve taking into account the entire circulation system resistance including a clean filter, strainer, heater, piping, valves and elbows. The static suction lift is not reflected in the curve. The dashed lines show the effect of increased filter resistance on the system head curve.
FIG. 6 also shows the typical operating characteristics of a centrifugal pump and the curve is labeled H.Q. System performance may be evaluated by comparing the H.Q. curve and the system head curves. With a clean filter, a head of about 21 feet would result in a flow of about 88 gallons per minute; however, with a dirty filter, a head of 54 feet develops a flow rate of about 25 gallons per minute. Thus, the filter itself can result in increased pressure drops of over 33 feet.
As a result of this increased pressure drop across the filter, prior art designers have considered it essential that the pump operating characteristics provide sufficient head to overcome this pressure drop.
In an attempt to increase pump efficiency and thereby reduce the energy consumption, attempts were made to redesign the pump. A smaller diameter impeller reduced the energy consumption but simultaneously reduced the pumping capacity to an extent that the head was not sufficient to prime the system and the circulation rate was not sufficient for vacuuming the pool and the pool could not be quickly cleaned after a storm or during heavy use. In addition, the lower circulating rate could not meet certain governmental codes which require that a filtering system be capable of circulating the entire pool capacity during periods of time varying from eight to twelve hours depending upon the particular code involved.
Another energy saving expedient was to provide a slower operating motor; however, this resulted in the same problems experienced with the smaller diameter pump impeller, namely insufficient head for priming and insufficient flow rate for vacuuming, and was not a satisfactory solution. In addition, this expedient was summarily dropped because the pump could not provide sufficient head to overcome the filter pressure drop previously described. Thus, the swimming pool industry lived with the problem and used inefficient pumps that had sufficient capacity for maximum demand.